Mold wash composition

ABSTRACT

A mold wash consisting of a vehicle wherein there is held in suspension a mixture of a refractory base, a suspension agent, a binder and a readily volatilized constituent selected from the group consisting of metals and complex metal flourides. The wash is characterized in that the readily volatilized constituent reacts to form a refractory. A preferred constituent is potassium zirconium flouride.

United States Patent 1 Howells a 1 Nov. 6, 1973 1 MOLD WASH COMPOSITION[75] Inventor: Norman C. Howells, Conneaut, Ohio [73] Assignee: Exomet,lncorporated,Conneaut,

Ohio

221 Filed: July 19,1971

211 Appl.No.: 164,030

[52] US. Cl l06/38.23, 106/38.24, 106/38.25, 106/214, 106/237, 106/238,106/241,

[51] Int. Cl B28b 7/38 [58] Field of Search l06/38.22, 38.23, 106/38.24,38.27, 38.5 R, 38.5 D, 38.25, 214,

[56] References Cited UNITED STATES PATENTS 1,725,039 8/1929 Williams106/38.27

2,652,312 8/1953 Fink'..'; l06/38.5 D 3,081,177 3/1963 Garay et a1.106/38.5 D 3,212,145 [0/1965 Green 1 [06/3822 3,275,460 9/1966.lcanneret 106/38.22

Primary Examiner-L0renz0 B. Hayes Att0rneyRonald B. Sherer et al.

57 ABSTRACT 5 Claims, N0 Drawings BACKGROUND OF THE INVENTION Thisinvention pertains to the art of metal founding. In the foundry and thesteel mill, it is common practice to coat the interior surfaces of themold with a wash to prevent intrusion of the molten metal into pores,cracks and the like on the surfaces of the mold cavity that will contactmolten metal. Mold washes, as the coatings are commonly called, areapplied to sand mold cavities for making castings of a specific shape aswell as to the interior of iron ingot molds used in the steel mill.

Prior art mold washes, such as disclosed in U. S. Pat. Nos. 3,121,269and 3,21 1,560, are painted or sprayed on the mold cavity surface anddried to form a continuous refractory surface over the sand or metal.These washes can be mechanically cracked prior to casting of the metalwith the result that the molten metal enters cavities in the refractoryto contact the sand or metal mold surfaces. lnthe sand molds, iron,steel or other high melting point metal produces a dense, very adherentmixture of metal and entrapped sand on the surface of the casting whichis difficult and expensive to remove. In the case of cast iron or steelmolds, the ingots become difficult to strip and generally containsurface defects. These defects require extensive salvaging operationssuch as chipping, grinding, burning or machining, thereby decreasingproduction and increasing cost of the castings or ingots poured.

BRIEF DESCRIPTION OF THE INVENTION In order to avoid the above describedproblems and produce an improved mold wash, it has been discovered thatwhen a readily volatilized metal or metal compound component, thatreacts under heat to form a refractory oxide, is added to a basic w,mixture of a refractory base, binder, and suspension and the dry mixsuspended in a suitable vehicle is applied to the mold surfaces, highmelting point metals can be successfully cast relatively free of grosssurfaces defects. The wash reacts under heat liberated by the metalentering the mold to prevent intrusion of metal into discontinuities inthe mold cavity surface by forming a refractory oxide.

Therefore, it is the primary object of this invention to provide animproved mold wash. 1

It is another object of this invention to provide a mold wash useful forcasting metals having high melting points.

It is a further object of this invention to provide a mold wash for usein mold cavities of sand or iron used for the casting of ferrous metals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The mold washes of thepresent invention are unique in that the volatile additive reacts underthe heat of the molten metal to form a continuous refractory surface onthe mold cavity.

The broad compositional ranges of the present invention are:

% by weight Suspension agent 0-6 Binder 0.2- Volatile Constituent0.25-95 Base 0-98 The above compositional ranges are for the dryingredients which are normally suspended in a vehicle such as water,isopropyl alcohol, ethyl alcohol, methyl alcohol, naphtha, or mixturesthereof.

The preferred suspension agent is one thatyexhibits I thixotropicproperties so that settling is inhibited and the wash can easily beapplied. A seaweed extract called carrageenen is particularly effectiveas a suspension agent. Sodium alginates and bentonite clays have alsobeen effective. Colloidal silica and fly-ash from a coal firedelectricalgenerating station are satisfactory suspension agents.

A preferred binder is phen ol formaldehyde (phenolic resin). Shellacflakes (in alcohol vehicle), drying oils known in the trade as coreoils, dextrine, polyvinylpyrolidone and mixtures thereof and with thephenolic resin are also very effective binders.

Refractory bases include zircon flour, chromium ore, silica flour,graphite, aluminum oxide, and mixtures thereof.

- aluminum flouride, sodium aluminum flouride, potas- In order for moldwashes of the present invention to succeed, they must contain a readilyvolatile ingredient that will react to form a refractory oxide to adhereto mold cavity surfaces or react with the mold cavity surface to formthe refractory oxide.

sium chromium flouride, and the preferred potassium zirconium flouride.It is also' possible to use a metal such as magnesium that is readilyvolatilized and forms a refractory oxide on the mold cavity surface.

A series of mold washes were formulated and tested in a mold usingmolten gray iron. The wash is placed on' a core made from a mixture of:

3% Phenolic resin 3% Dextrose with amonia salt 1% Gelatinized corn flour5% Water 88% Sand The cores in the form of sticks were baked and thewash applied in a wet coating about 1/32 inch thick. After coating, thecores were rammed in place at the bottom of a mold cavity about 7 inchesin diameter and about'30 inches high, the cavity being bottom gated.Molded exothermic riser sleeves were used in the cavity to lengthen thetime that the 15 to 30-inch high column of metal would be molten. Thelonger contact time for the molten metal to the core provides a morerigourous test than normally used in the foundry.

Table I sets forth a series of washes that were used in the foregoingcore test and showed no penetration of Wash No. (percent by weight)Constituent l 2 3 4 Carrugeenen Colloidal silicu.. Fly ash Phenolicresin Dextrine tttttt She|lac..... Core oil tttttttttttttttPolyvinykpyrolidone.

K rlw;

Zircon flour. Chrome ore....

The washes of Table I were formulated and numbers 1 through 8 weredispersed in water as a vehicle whereas numbers 9 and 10 were dispersedin an ethyl alcohol vehicle. The ratio of dry ingredients to vehicleshould range from 1 k 3 'rto l by volume depending upon the method ofapplication, a good spray mixture being 2 1a; 1 respectively. In washNo. 9, silica flour can be substituted for zircon flour in the ration of1 part silica flour for 2 parts zircon flour, serving as both arefractory and a suspension agent.

In Table l washes 1-5 were also effective when tested on the interiorsurface of a cast iron ingot mold into which a ferrous melt was poured.

It has also been shown that in wash No. 9, hydrated aluminum chloridecan be used alone or in combination with thephenolic-polyvinylpyrolidone system as a binder agent.

In all of the washes the key is the volatile constituent that reacts toform a refractory oxide. The balance of the composition provides themedium as needed for this reaction to take place.

Other volatile flourides, such as sodium zirconium flouride, can beused.

Having thus described my invention, the following is desired to besecured by Letters Patent of the United States.

I claim:

1. Dry ingredient mixture for a mold wash for use in preventingintrusion of molten metal into surface openings on a foundry core oringot mold consisting essentially of 0.25 to 95 percent potassiumzirconium flouride; 0.2 to 20 percent of a binder selected from thegroup consisting of phenolic resin, dextrine, shellac, drying oil, andpolyvinylpyrolidone; balance zircon flour.

2. A mold wash containing the dry mix .according to claim 1 dissolved ina vehicle selected from the group consisting of water, ethyl alcohol,isopropyl alcohol, methyl alcohol and mixtures thereof.

3. A mold wash according to claim 1 wherein silica flour is substitutedfor zircon flour on a 1 to 2 ratio respectively.

4. A mold wash according to claim 2 wherein the 1 1/2 to 3 1/2 parts dryingredients are mixed with'l part vehicle.

A maia'wah' eonstsrmgsrmts '10 percent by weight binder selected fromthe group consisting of phenolic resin, dextrine, shellac, drying oil,and polyvinyl pyrolidene and 98 to percent by weight potassium zirconiumflouride.

2. A mold wash containing the dry mix according to claim 1 dissolved ina vehicle selected from the group consisting of water, ethyl alcohol,isopropyl alcohol, methyl alcohol and mixtures thereof.
 3. A mold washaccording to claim 1 wherein silica flour is substituted for zirconflour on a 1 to 2 ratio respectively.
 4. A mold wash according to claim2 wherein the 1 1/2 to 3 1/2 parts dry ingredients are mixed with 1 partvehicle.
 5. A mold wash consisting of 2 to 10 percent by weight binderselected from the group consisting of phenolic resin, dextrine, shellac,drying oil, and polyvinyl pyrolidene and 98 to 90 percent by weightpotassium zirconium flouride.